Water quality impacts of misconnections

In the UK misconnections contribute to failing water quality standards in many rivers and beaches. Water quality should met Water Framework and Bathing Water Directives standards for phosphorus, dissolved oxygen, ammonia, certain chemicals and pathogens that present a health risk to water users. The environmental regulators are still investigating the ‘reasons for failure’ for many water bodies. It is difficult to understand the impacts from misconnections in urban watercourse or beaches because of complexities and variety of sewer networks, property types and other inputs. Often the more obvious impacts from foul misconnections into surface water sewers are masked by wetter weather and become very much more apparent in drier weather. In contrast the impact of clean misconnections become really obvious in very wet weather. Urban watercourses and beaches can also be impacted by other factors such as engineering (morphology), overflows from combined sewers, land use and activity which all make it difficult to assess the individual impact from misconnections.


Misconnections of sewage, especially from washing machines and toilets, contain phosphorus which is a nutrient that causes enrichment in water also known as eutrophication.  This enrichment affects the natural ecology and leads to excessive algae or plant growth. Within sewage dishwasher and laundry detergents, food and drink additives and faeces and urine as well as the dosing of drinking water supplies are all significant sources of phosphates.  Phosphorus concentrations in our rivers has increased significantly between the 1950 and the 1980s but sewage treatment and other measures has since the 1990s reduced the total river lengths most adversely effected.  Misconnections clearly contribute to phosphorus levels but also the excessive algal growth can look unsightly.

Faecal Indicator Organisms (FIOs)

So called Faecal Indicator Organisms are regarded as an indicator of the presence of more dangerous bacteria from faeces.  Sewage discharges into urban watercourses or beaches via surface water sewers contain FIOs at significant concentrations. This has potential impacts on public health and economic impacts on tourism.  Sewage treatment reduces FIOs concentrations greatly but foul misconnections bypass sewage treatment processes entirely.

Compliance with the current Bathing Water Directive (cBWD) standards is good (98% of designated waters in England and 99% in Wales complied with mandatory standards).  However in 2015 new standards are being introduced that are twice as strict and compliance will therefore decrease. 

Sanitary pollutants

Sanitary pollutants include ammonia and other compounds reduce levels of dissolved oxygen in water.  Aquatic organisms use dissolved oxygen in water for respiration.  Misconnections contain ammonia and a whole range of organic matter typically found in sewage.  In addition organic matter can reduce light levels further reducing the production of oxygen via photosynthesis by plants.  A reduction in dissolved oxygen can cause stress and lethal effects on aquatic life.  Ammonia is produced when organic wastes are broken down and this reduces dissolved oxygen levels further.  Un-ionised ammonia is also hazardous due to its toxic and sub-lethal impacts on fish and macro invertebrates.

Sanitary pollutants are generally an issue for rivers and smaller watercourses.  The actual effects of ammonia and dissolved oxygen concentrations are related to acidity (pH), temperature and flow.


The rise in manufacturing and other industries, transport and more-intensive agriculture has resulted in an increasing use and release of chemicals into the environment.  Chemicals covered under the Water Framework Directive are those that are thought to cause a risk to the environment or human health. 

Our understanding of the presence or otherwise of chemicals in the environment is patchy, especially for those that enter watercourses via diffuse routes such as via misconnections and urban drainage.  There are a group of substances that are commonly used for domestic purposes and therefore found in sewage.  These include flame retardants, biocides, medical compounds and chemicals found in new clothing. 

Of particular relevance to misconnections are the following chemicals;

1)  Nonyl-Phenols (NPs) and their Ethoxylates (NPEs) are Priority Hazardous Substances which are restricted under UK and EU legislation.  Nonyl-phenols have been used as emulsifiers and modifiers in paints, pesticides, textiles, and some personal care products. The EU has restricted the use of NPs but these chemicals are commonly found in imported clothing and released into the water environment via washing clothes.  It is estimated that imported clothing might account for up to 20% of NP and NPE in UK rivers.  Sewage effluent is also considered to be a major source of NP & NPEs.  On average, based on Water Company investigations, circa 45% of all misconnections found are from washing machines and sinks.

2)  Tributyl tin compounds (TBT) are biocides with many uses. They are banned but still found to be present in textiles and recent studies have shown the presence of TBT in imported clothing. Because they are persistent and accumulate in species they give rise to long term ‘legacy’ problems in river sediments. Sewage treatment works appear to be significant current source which implies misconnections are important sources as well.

3)  Di(2-ethylhexyl)phthalate(DEHP) is a plasticiser used mostly (97%) in polymer products often found in buildings and electrical goods especially the plastic PVC. There are other uses (3%) of DEHP in products such as coatings, adhesives, inks, fillers and ceramics. This widespread use of products containing DEHP results in its presence in wastewater from households as well as commercial premises. The use of DEHP has been restricted since February 2013 but there remains a significant ‘legacy’ problem from existing products.

4)  Tryclosan is a biocide included in many personal care products and household plastics from where it enters the sewerage system. There are a number of high risk products on the market such as toothpaste (~20 products) and hand wash (~35 products) as well as surgical uses in hospitals. 

5)  17alpha-ethinylestradiol (EE2) is a synthetic steroid used in most oral contraceptives and has other medical uses such as for various gynaecological disorders and post-menopausal breast cancer. EE2 also enters the aquatic environment via sewerage systems.

6)  Brominateddiphenylether (BDPE is a flame retardant that has been banned for use in the European Union. It is a persistent, accumulates in the environment and so has significant ‘legacy’ issues.  By far the largest source is domestic sewage and sources. It is thought that concentrations are the result of washing clothing or textiles that has been exposed to the dust of soft furnishings that containing the fire retardant chemicals.

Other impacts

In addition to the impacts set out above misconnections also look bad due to eutrophication and sewage.  These visual impacts are often made worse in drier weather when sewage fungus or the effects of eutrophication become more apparent.  Use of urban streams also increases in warmer drier weather.

‘Clean’ misconnections also reduce sewerage capacity in wetter weather.  Whilst some infiltration from groundwater and rainfall is inevitable, prolonged periods of wet weather, such as that experienced in the summer of 2012 indicate the true scale of the problem.  These factors can lead to development pressure on infrastructure in some areas which in turn will affect growth. Increased foul sewer flows also result in more overflows to water bodies and in some cases even to properties.  Rain water entering foul sewers also increases the pumping and treatment costs and adds significantly to energy use.